The present invention relates generally to an x-ray tube target assembly, and, more particularly to a composite target assembly with improved thermal and mechanical robustness.
X-ray tubes are well known and widely utilized in a variety of medical imaging fields, medical therapy fields, and material testing and analysis industries. They are commonly comprised of both an anode assembly and a cathode assembly. X-rays are produced when electrons are released in a vacuum with the tube, accelerated and then abruptly stopped. The electrons are released from a heated filament. A high voltage between the anode and the accelerates the electrons and causes them to impinge on the anode. The anode is also referred to as the target since the electrons impact the anode at the focal spot.
In order to dissipate the heat generated at the focal spot, X-ray tubes often incorporate a rotating anode structure. The anode in these arrangements commonly comprises a rotating disc so that the electron beam constantly strikes a different point on the target surface. Although these methods can reduce the concentration of heat at a single spot on the target surface, there is still considerable heat generated within the target. The rotating disc and rotating shaft assembly may, therefore, be exposed to high temperatures in addition to significant temperature fluctuations between operational states. These temperature fluctuations, in addition to the mechanical stresses associated with rotation of the target disc, can expose the components of a target assembly to considerable induced stresses.
Present x-ray tube target geometries consist of planar disks that extend from the bore of the target outward. Material strain in the bore region can be of significant concern. Material strain in the bore region may cause loss of balance in mechanically attached target-stud joints. It may also result in cap to graphite separation in the case of composite metal-graphite targets. As the performance demands of x-ray tubes are increased, the operating stresses generated by thermal and mechanical loadings on target assemblies will continue to increase. Although these increasing operating stresses may be at least partially addressed through the variance of material properties of the target components, the continuously increasing performance requirements may quickly strain any material property limits.
It would, therefore, be highly desirable to have a target bore strengthening method whose methodology did not rely solely on the improvement of material property. It would be further desirable to have a target assembly with improved bore strength that was compatible with metal-graphite composite targets.